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E NCODING Encoding is the process which assigns ones and zeros (stream of bits) for every quantization level. The number of bits assigned for each level ( n ) depends on the levels’ number ( L ) ; such that L= 2^n.

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I DEAL ADC Q = Δ=quantization step = full scale / levels’ number. In an ideal analog-to-digital converter, the quantization error is uniformly distributed between –Δ/2 and Δ/2. The resolution of the ADC is the smallest detectable change in voltage.

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ADC0804 A NALOG TO D IGITAL C ONVERTER ADC0804 is a 20-pin IC with an 8-bit resolution. The analog input voltage range is from 0 V to 5 V, with 15 mW power consumption and 100 us conversion time.

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SAR ADC It is one of the popular ADCs for 8-16 bits. It has moderate conversion speeds ; the conversion time is around 1 Us. It doesn’t consume a lot of power and its cost is low in comparison with the other types. On the other hand, it requires a sample and hold circuit and it can have missing output codes.

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T HE B LOCK DIAGRAM OF SAR ADC AND ITS FLOW CHART

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D ESCRIPTION OF OPERATION A successive approximation ADC works by using a digital to analog converter (DAC) and a comparator to perform a binary search to ﬁnd the input voltage. A sample and hold circuit (S&H) is used to sample the analog input voltage and hold (i.e. keep a non-changing copy) the sampled value whilst the binary search is performed. The binary search starts with the most signiﬁcant bit (MSB) and works towards the least signiﬁcant bit (LSB). For a 8-bit output resolution, 8 comparisons are needed in the binary search, taking a least 8 clock cycles. The sample and hold circuit samples the analog input on a rising edge of the sample signal. The comparator output is a logic 1 if the sampled analog voltage is greater than the output of the DAC, 0 otherwise.

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D IGITAL T O A NALOG C ONVERSION ( DAC) Digital to analog converter (DAC) is the device which converts digital signals to analog ones. Most of the DACs consist of a network of resistors and analog switches. The switches control the currents or voltages that are derived from a particular reference voltage and provide analog output current.

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R-2R DAC The Block diagram of R-2R DAC is as shown below: The analog output is given by the following equation: The highest resistance value is only 2R and thus requires an area inside the IC less 8 times than that of the weighted resistor DAC which highest resistance is 16R.

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The DAC analog output is represented by current. This current is the ratio of the input code to the full scale voltage (Vref) as given in the following equation: So, an operational amplifier is needed to convert the current to voltage level.

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T HE G ENERAL P URPOSE ( DAC 0800) The block diagram of DAC 0800 is as shown below: It’s clear that it’s a 8-bit DAC with 16 pins IC. The conversion time is around 100ns.

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B IPOLAR / U NIPOLAR DAC S For unipolar DACs, the output voltage is given by: For bipolar DACs, the output voltage is given by: